This invention relates to molded polyolefin and polyphenyloxide products and to methods for their production. The invention has application to the production of products of a variety of types but will be described with respect to vehicle parts, particularly parts of that type which are used in vehicle interiors and which therefore require a pleasing exterior appearance.
Parts of the type described may comprise, for example, panels which are attached on the inside of automobile doors. The doors typically are made of sheet metal and plastic panels are attached directly to the steel or other sheet metal support to achieve a pleasing interior appearance. U.S. Pat. No. 4,766,025 describes such products and a method for their manufacture. In the background section of the patent, reference is made to the formation of discrete plastic parts followed by assembly in a piece-by-piece manner during installation. The patent then goes on to describe a method wherein a vinyl sheet is stretched over a mold cavity, heated, and then pulled into the cavity using a vacuum. Moldable polyvinylchloride or polyurethane is then injected to form the part in one piece comprising the plastic body and the vinyl skin.
Attempts have also been made to make automobile door panels and other parts using expanded polystyrene. In this system, for example as reported in the March, 1996 issue of "Plastics Technology", an EPS part is first molded, a film of polystyrene is located in a mold along with the previously molded EPS part, and steam is introduced to bond the two materials together.
These prior art systems are characterized by certain disadvantages. Thus, parts made using injection molded PVC, polyurethane and the like are relatively heavy. The EPS parts are more lightweight but production methods are unduly complex leading to additional manufacturing costs. Furthermore, difficulties are encountered during installation of the EPS parts since the plastic is not sufficiently strong for use of screws and other fastening methods commonly used for assembly of the parts with a steel or other sheet metal door or the like.